Microbial production of lactate-enriched poly[(R)-lactate-co-(R)-3-hydroxybutyrate] with novel thermal properties

Considerable enrichment of the lactate (LA) fraction in Poly[(R)-LA-co-(R)-3-hydroxybutyrate (3HB)] has been achieved, reaching up to 47 mol % from the previous 6 mol % [S. Taguchi et al. Proc. Natl. Acad. Sci. U.S.A. 2008, 105 (45), 17323-17327], when recombinant Escherichia coli W3110, harboring the LA-polymerizing enzyme gene together with three genes for supplying monomers, lactyl-coenzyme A (CoA), and 3-hydroxybutyryl-CoA, were grown on glucose under anaerobic conditions. The molecular weights of the copolymer were M(n) = 1.5 x 10(4) g/mol and M(w) = 2.0 x 10(4) g/mol, respectively. Notably, alkaline-hydrolyzed product analysis revealed that only the (R)-enantiomer of LA was incorporated in the copolymer. Furthermore, the triad sequence of LA-LA-LA was clearly detected in the polymer chain based on NMR analysis. A remarkably contrasting melting temperature was observed between the copolymer obtained here P[(R)-LA-co-(R)-3HB] (157 degrees C) and the chemically synthesized P[(S)-LA-co-(R)-3HB] (105 degrees C) with similar monomer composition.